The Advantages of cDNA in U.S. Patent Claims

For many years, biotechnology companies routinely sought patent protection for newly discovered genes. That changed dramatically in 2013 when the Supreme Court decided Association for Molecular Pathology v. Myriad Genetics. The Court held that a naturally occurring DNA sequence generally does not become patent eligible merely because it has been isolated from its natural environment. As a result, patent practitioners have increasingly focused on other forms of nucleic-acid protection.

One of the most important of these is complementary DNA, or cDNA. For inventions involving eukaryotic genes, cDNA often provides one of the most straightforward paths to a patent-eligible nucleic-acid composition claim.

What Is cDNA?

To understand why cDNA can be important, it is helpful to first review how genes are expressed.

In eukaryotic organisms such as animals and plants, genes frequently contain coding regions known as exons separated by non-coding regions known as introns. When a gene is transcribed, both the exons and introns are initially copied into RNA. Before that RNA is used to produce a protein, the introns are removed and the remaining exon sequences are joined together through a process known as splicing. The resulting molecule is referred to as mature messenger RNA, or mRNA.

Scientists can use an enzyme known as reverse transcriptase to produce a DNA copy of this mature mRNA. The resulting molecule is known as complementary DNA, or cDNA. Because cDNA is derived from processed mRNA, it generally contains the joined exon sequences but lacks the introns present in the original genomic gene.

Why cDNA Can Be Different from the Natural Gene

The distinction between genomic DNA and cDNA is often critical. A naturally occurring eukaryotic gene may contain numerous introns interspersed among its coding regions. By contrast, the corresponding cDNA will generally contain only the exon sequences that remain after RNA processing.

As a result, the cDNA frequently possesses a different nucleotide sequence and a different structure from the genomic DNA found in nature. Although both molecules may ultimately direct production of the same protein, they are not necessarily the same nucleic acid. This distinction formed an important part of the Supreme Court's analysis in Myriad.

The Significance of Myriad

In Myriad, the Supreme Court held that naturally occurring DNA generally is not patent eligible merely because it has been isolated from a chromosome. At the same time, however, the Court distinguished cDNA from naturally occurring genomic DNA.

 The reason was straightforward. In many cases, cDNA lacks the introns present in the corresponding genomic gene. The Court viewed this structural difference as sufficient to distinguish many cDNAs from naturally occurring DNA.

As a result, cDNA often occupies a much stronger position under §101 than a claim directed to the corresponding natural gene.

An Important Qualification

The Myriad decision does not mean that every molecule labeled "cDNA" is automatically patent eligible. The key issue is whether the cDNA differs structurally from the naturally occurring gene. If the corresponding gene contains no introns, a cDNA may be identical or nearly identical to the naturally occurring sequence. Likewise, some very short cDNA fragments may not possess the structural differences that supported patent eligibility in Myriad.

Nevertheless, for many eukaryotic genes, introns are present and the resulting cDNA will differ from the genomic sequence. In those circumstances, cDNA often provides one of the clearest paths to a patent-eligible nucleic-acid composition claim.

Beyond the cDNA Itself

The advantages of cDNA extend beyond claims directed solely to the nucleic acid. Once a cDNA has been identified, it can often support several complementary claim types. Examples might include:

A cDNA comprising the nucleotide sequence of SEQ ID NO: X.

A recombinant host cell transformed with a cDNA comprising the nucleotide sequence of SEQ ID NO: X.

A method of producing Protein X comprising expressing a cDNA comprising the nucleotide sequence of SEQ ID NO: X in a host cell and recovering Protein X.

These examples illustrate an important principle of biotechnology patent practice. The same cDNA may support protection at several levels, including claims directed to the nucleic acid itself, engineered cells containing the nucleic acid, and methods employing the nucleic acid to produce a commercially valuable

Disclaimer: This piece is provided for general informational purposes only and does not constitute legal advice. Patent issues are often complex and highly fact-specific, and no one should act on general information of this kind without consulting qualified patent counsel regarding the particular circumstances involved.